The present invention relates to electric solenoids as used in mechanical linear actuators; more particularly, to such solenoids as may be required to operate in moist conditions or over a wide range of temperatures; most particularly to such a solenoid having vents which impede the entrance of particles of dirt, including droplets of liquids, into the interior, while simultaneously permitting the draining and evaporation of condensation.
Electric solenoids are well known in electrical engineering and are widely used as actuating components in electromechanical linear actuators. A typical electric solenoid consists of a plurality of windings of an electric conductor about north and south polepieces. When current is passed through the windings, a characteristic toroidal magnetic field is produced having field lines at the axis which are parallel to the axis. A ferromagnetic armature is slidably disposed in an axial bore in the polepieces. An axial force is exerted by the magnetic field on the armature which tends to displace the armature axially. The strength of such force can be varied by varying the current flowing through the windings. Thus, by attaching the armature to a shaft, a solenoid may be adapted readily to provide linear mechanical actuation of a device to which it is attached. Solenoids are probably the commonest type of such actuators in use today.
Solenoids rely for efficiency on having very close tolerances among the various mechanical and electrical components, and they are therefore susceptible to failure if foreign particles, corrosive gases, corrosive solutions, or moisture are allowed to enter and remain within the solenoid housing. Some known solenoids are provided with housings which are hermetically sealed in an effort to prevent any contamination from ever entering. However, a sealed housing presents a dilemma. To the extent that such a housing succeeds in keeping contamination out, it also traps within itself any contaminant that is able to enter despite the housing design. Thus, contaminants, and especially water, may become trapped within a solenoid and may either short out electrically or corrode electrical and mechanical elements critical to the operation of the solenoid.
What is needed is an improved solenoid wherein particulates and droplets of moisture are impeded from entering directly, but wherein the interior of the solenoid is vented to the exterior to permit drainage and evaporation of moisture from within the solenoid.
The present invention is directed to an improved solenoid for providing linear actuation. The outer polepiece of the solenoid is provided with a plurality of radially-dispersed labyrinthine passageways in communication between the exterior of the solenoid and the interior region comprising the armature and the interior of the windings. The polepiece is further provided with at least one passageway in communication between the exterior of the solenoid and the outer periphery of the windings within the housing. The two sets of passageways impede particles and droplets of moisture from entering the solenoid, while simultaneously permitting moisture such as condensation within the solenoid to drain or to evaporate and escape.